Paper machines are often subject to problems such as barring or streaking in the output paper sheet. In the prior art, such problems are conventionally addressed by techniques such as substitution of newer, more rigid headbox components; stiffening of the headbox support structure; alterations to the headbox approach and screen piping, changes to the headbox overflow piping; grinding and polishing of the fan pump internals; adoption of newer more flexible slice structures; etc. Although various combinations of these techniques can yield significant sheet quality improvements, problems such as streaking often remain.
The inventors have traced such problems to factors such as excessive surface irregularities (waviness) in headbox components, especially the apron floor. Conventionally, a headbox apron floor is finished in a sequence of planing (or milling), grinding, mechanical polishing and electro-polishing steps to produce a uniform flat surface. But, these time consuming steps do not appear to yield surfaces which are flat within the tolerances which the inventors believe to be desirable in overcoming the foregoing problems. The inventors have developed new techniques for measuring various paper machine headbox components to high degrees of accuracy; detected a need for more accurate machining of such components to tolerances which have not previously been attained; and, developed techniques for such machining which eliminate the need for mechanical or electro polishing.